I suppose you could make an actual 1 to 1 scale model of your window layout. This seems excessive to me. I agree that communication with your printer about specific scaling requirements they might have is important prior to job setup so you can accommodate their needs before putting in too much work on the project.
Scalability in Illustrator can be cumbersome when working in our western style of feet and inches. The metric system is far easier in this regard- you just move the decimal place. CAD software is designed to work in scale. With Illustrator you have to do it pretty much on your own.
One way to approach this is to convert everything to inches only- so your first panel is 22'6" x 6'6". This would be (22.5 x 12)=270 inches wide x (6.5 x 12)=78 inches tall. At a 1/10th scale this would be 27 inches x 7.8 inches
I would actually make the scale 1"=1'. Your first panel would be 22.5 inches x 6.5 inches. It seems easy to keep track of things- for instance if you want lettering to be 1' tall you simply make it 1" tall. I would set it up all in one document with artboards sized to your window sizes (with or without the scale- your choice).
Here is a pic of my artboards (at 1"=1' scale)
To get the lettering or image sizes you can simply look in the transform panel with an object selected. Something whose W value is 16.54 inches and Y value is 5.32 inches in the transform panel would be 16.54 ' x 5.32' when printed. Unexpanded text is different in that the Transform Panel W and Y values will show larger than the actual text size (to account for acsenders and descenders). You can draw a throw away rectangle over the text and look at it's values to get an actual lettering height (once the text is expanded it will show it's size accurately in the Transform Panel).
For the mock up I just made a larger artboard behind the others and gave it a gradient fill. I am not sure how much this would need to embellished for your needs.
One thing which was not mentioned in your question is if these window panels are going to be all one piece (a 22'6"x 6'6" sticker ?) or if they will be smaller separate stickers that would be combined on one window. In that case I would still use this overall layout so you can see the whole project, then maybe create artboards for each different sticker and copy paste from the big layout for the individual print jobs.
The only other thing I would add is that it will be important to keep your file structure and organization sound. Use layers and sublayer organization so things are easy to find as you go along and also easy to lock or hide.